Hot work steel



Patented Sept. 8, 1936 PATENT OFFICE nor WORK STEEL Frederick F. McIntosh, Glen Osborne, Pa., as-

signor to Crucible Steel Company of America, New York, N. Y., a corporation of New Jersey No Drawing. Application August 9, 1934,

Serial No. 739,150

4 Claims. (01'. 75-120) This invention relates to hot work steels and hot work tools made therefrom.

Hot work steels, used for making tools for shaping or cutting hot metal, such as dies,

5 punches, shears, and the like, to be satisfactory must possess adequate strength and toughness at the elevated temperatures of the tools resulting from working conditions, which may vary from room temperature up to red heat, depend- 10 ing upon the time of contact with the metal which is being fomed or cut, the character of work which the tool does, the time of contact with the metal which is being formed or cut, and upon whether or not a cooling medium is used.

15 They should likewise embody the ability to resist softening under the heating of use, together with resistance to fire checking resulting from rapid heating and cooling, andresistance to abrasion in service. I

20 Many different steels have been proposed for hot work applications, but none of those available prior to this invention has embodied a detion for some types of service conditions.

It is among the objects of this invention to provide hot work steels embodying a combina- 5 tion of mechanical properties more suited to hot work tools than those available heretofore, which are of simple and relatively inexpensive composition, and are characterized, among other things, by their ability to retain cutting edges for long 40 periods of time, and by excellent structural stability at the temperatures encountered in hot work uses.

The invention is predicated upon my discovery that steels containing about 0.3 to 0.75 per 45 cent of carbon, about 5 to 9 per cent of chromium, about 1 to 2.25 per cent of manganese, about 0.3 to 1 per cent of molybdenum, and about 1 to 3 per cent of nickel are especially adapted for the making of hot work tools, and that tools 5 made from such steels embody characteristics of such nature as to render them more satisfactory than those used heretofore.

Within the foregoingrange of composition especially desirable results, particularly for shear 55 knives and similar articles, are obtained by the In some instances no steel has met with complete satisfacuse of steel containing about 0.4 to 0.5 per cent of carbon, about 6.25 to 7.75 per cent of chromium, about 1.1 to 1.25 per cent of manganese, about 0.5 to 0.75 per centof molybdenum, and about 1.25 to 1.75 per cent of nickel.

The steels provided by the invention are characterized by air hardening properties, and one of their particularly desirable properties is that they do not require hardening at high temperatures, which is contrary to the case of many prior 10 hot work steels. That is, many hot work steels, especially those of the tungsten type, must be heated to a temperature of 2000 F. or higher to harden them. The steels embodied in the present invention can be air hardened from about 1800 F. The advantages of this lower hardening temperature and of air hardening itself, for these purposes will be understood by those skilled in the art.

The steels provided by the invention are likewise characterized by structural stability under the temperatures encountered'in use. One indication of this structural stability appears from the fact that the best results in the practice of this invention are obtained when tools made from steels of the foregoing composition are tempered at temperatures as high as 1300 F. ,In contrast, most prior hot work steels are tempered, a'fter hardening, at about 1100 F. The higher tempering temperatures of the steels provided by the invention is an indication of greater structural stability at elevated temperatures.

In addition, the steels used in the practice of this invention possess desirable strength and toughness at the temperatures encountered in use, and they are satisfactorily resistant to fire checking and abrasion. In consequence of these properties hot work tools made from steels of the foregoing compositions are particularly adapted to meet a wide variety of service conditions, and actual experience has shown that they are much better suited to these purposes than the steels previously available.

The best criterion of the ability of a steel to serve for hot work purposes is its actual performance under difficult and exacting service conditions, and actual experience, as just noted, has shown the tools provided by this invention to be superior to those heretofore available. As an illustration, one of the largest steel mills in this country has in the past experienced serious delays due to the lack of a hot work steel which would perform satisfactorily in the form of shear knives used on flying shears forming a part of the 18 inch mill at that plant. This mill has a capacity of 1000 tons of steel in an eight-hour turn. Using the best hot work steels available prior to this invention it was necessary to grind the shear knives two or three times a week, and breakage was frequent.

0n the other hand, shear knives made in accordance with this invention have overcome those difliculties, and since their installation the regular practice in that mill has been to grind the knives only once a week, at the time of shut down on the mill. No breakage at all has been experienced, and the operators of the mill have stated that the performance of the knives made in accordance with this invention is 100 per cent better than any hot work steel which they have used previously. A typical analysis of steel in accordance with the invention used in the manufacture of those shear knives is 0.46 per cent of carbon, 6.79 per cent of chromium, 1.31 per cent of manganese, 0.6 per cent of molybdenum, and 1.52 per cent of nickel.

It appears from the foregoing actual experiences that the steels, or tools, provided by this invention embody improved structural stability and greatly improved resistance to abrasion compared with prior steels, as indicated by the fact that the knives provided by the invention need be ground only once a week, whereas with shear knives made from prior art steels it was necessary to grind them two or three times a week, even using the best material then available for that purpose. The structural stability and the fact that the steels provided by this invention embody adequate strength and toughness under operating conditions is demonstrated by the fact that no breakage has occurred with the knives made from this invention. In contrast, the best available steel was subject to rather frequent breakage. Other advantages, improvements andbenefits resulting from the invention will be understood by those skilled in the art.

According to the provisions of the patent statutes, I have explained the principle and construction of my invention and have described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

1. As a new article of manufacture, a hot work tool formed from a steel containing more than about 0.3 to 0.75 per cent of carbon, about 5 to 9 per cent of chromium, about 1 to 2.25 per cent of manganese, about 0.3 to 1 per cent of molybdenum, and about 1 to 3 per cent of nickel, and the remainder substantially iron.

2. As a new article of manufacture, a hot work tool formed from a steel containing about 0.4 to 0.5 per cent of carbon, about 6.25 to 7.75 per cent of chromium, about 1.1 to 1.25 per cent of manganese, about 0.5 to 0.75 per cent of molybdenum, and about 1.25 to 1.75 per cent of nickel, and the remainder substantially iron.

3. A shear knife formed from a steel containing about 0.4 to 0.5 per cent of carbon, about 6.25 to 7.75 per cent of chromium, about 1.1 to 1.25 per cent of manganese, about 0.5 to 0.75 per cent of molybdenum, and about 1.25 to 1.75 per cent of nickel, and the remainder substantially iron.

4. A hot work tool, such as a hot operated shear knife, formed from a steel containing about 0.5 per cent of carbon, 6.8 per cent'of chromium, 1.3 per cent of manganese, 0.6 per cent of molybdenum, 1.5 per cent of nickel, and the balance substantially iron.

FREDERICK F. MCINTOSH. 

